In conjunction with analyzing the blood gas content of arterial blood, it is necessary that a high degree of quality control be maintained in connection with the operation of the blood gas analyzer. A common approach for determining and monitoring the accuracy and precision of a blood gas analyzer is to utilize a control or standard sample of known composition. The control sample is inputted to the blood gas analyzer and analyzed to check whether the resulting output corresponds to the expected output. If the comparison does not indicate a correspondence, the blood gas analyzer may be calibrated to insure correspondence and proper operation of the analyzer.
To produce the control sample, a number of different tonometric apparatuses have been developed. In particular, a number of tonometers have been advanced for equilibrating a gas and liquid in a chamber for producing a control sample. In one class of tonometers, control samples are produced in modified syringes. In one of such syringetype tonometers, the tip of the syringe is inverted, or located downwardly relative to the opened end of the syringe barrel, and placed into a temperature-controlled chamber while the plunger of the syringe extends in the opposite direction away from the chamber. The equilibrating gas is inputted into the syringe tip through a valve. A venting hole is formed in the syringe barrel at the opposite end of the tip. Gas moves from the tip of the syringe to the opposite end of the syringe barrel and gas is able to exit the venting hole. In another syringe-type tonometer, the syringe is not inverted but, instead of entering the syringe tip, the equilibrating gas flows in the direction from the bottom of the syringe barrel to the syringe tip. This tonometer also includes a humidifying chamber in the syringe itself. In another group of tonometers, chambers or containers are utilized in preparing the equilibrated solutions and such solutions are removed from the chamber after the control sample has been made. With regard to such tonometers, it is common to use a conventional syringe, but only for removal of the control sample from the chamber, and not as a chamber in which an equilibrated solution is produced.
Each of these tonometers suffers from one or more drawbacks that reduce its effectiveness and operability thereby minimizing meaningful acceptance of the tonometer by potential users. In the case of previously devised syringe tonometers, a conventional syringe must be modified in order to provide required features associated with the tonometer operation. For example, a venting hole must be provided at the bottom end of the syringe in one case and, in the other, a syringe must be provided that is able to provide a humidifying chamber and house a pair of membranes. Additionally, problems can occur relating to valve leakage while the valve is attached to the syringe tip. And, in the case of equilibrating blood housed in the syringe, when it is necessary to remove air trapped in the syringe, the vent hole must be covered and the user may contact the blood to provide the covering. With regard to non-syringe tonometers, it is always necessary to remove the equilibrated solution from the chamber in which it was made so that it can be transported and inputted to the blood gas analyzer whereby diminution of the quality of the sample can occur during such a transfer of the sample.